From official forums:

Hey everyone, the lag from Reim has been getting worse. Tonight (2/4/2021), I see over 50 people in the area and the game is just grinding to a halt often.

We've made a lot of changes to try to accommodate the larger group hunts. We've worked on the room window and how the engine handles updates. We've updated how group contributions are handled, as well as how AoE spells are limited to help on how the messaging can create exponential strain on the game. We've talked with the groups who run Reim to try to limit their size. But it all hasn't been enough and the group size is bigger than ever. Moving forward, we're going to need to take more drastic measures, whether it's changing the mechanics of Reim or limiting group size. We've spent a lot of time and we've tried to work these issues out, but we can't allow this to cause issues with the game as a whole anymore.

If we're unable to come up with something fairly quick, we'll be temporarily closing down the area until we can complete it.

Wyrom, PM
...further down in same thread...

From Wyrom on discord.
We've worked things out with those running the hunt and I think we're all on the same page. We really don't want to discourage groups. We have put a ton of effort with trying to get this handled. It's not just Reim. It's the command queue, which is why guild night saw it. We also updated how the room window (StormFront) handles things, which was a big help. The game can clearly handle big groups, it's just when messaging is happening it gets exponential bad when group size grows too high.